SACA Process Control and Instrumentation 4

Question 1

In a cascade control system, which controller receives the process variable from the field sensor?

Accepted Answer

Secondary (slave) controller

Answer

In cascade control, the secondary (slave) controller measures the inner loop process variable and receives its setpoint from the primary controller.

Question 2

What is the primary purpose of a dead band setting in a process controller?

Accepted Answer

Prevent hunting around the setpoint

Answer

Dead band creates a neutral zone around the setpoint where no corrective action is taken, preventing excessive valve cycling or 'hunting.'

Question 3

An orifice plate differential pressure transmitter reads zero even though flow is present. Which fault is MOST likely?

Accepted Answer

Both impulse lines are open and equalized

Answer

If both impulse lines are open and equalized (e.g., isolation valves open and equalizer valve also open), the DP transmitter sees zero differential pressure.

Question 4

Which valve characteristic provides equal percentage of remaining flow change per equal increment of valve travel?

Accepted Answer

Equal percentage

Answer

An equal percentage valve changes flow by a fixed percentage of its current flow rate for each unit of stem travel, giving better rangeability at low flows.

Question 5

A HART communicator is connected to a 4-20 mA loop. What is the carrier frequency of the digital HART signal superimposed on the analog signal?

Accepted Answer

1200 Hz

Answer

HART uses Bell 202 FSK at 1200 baud (1200 Hz for mark, 2200 Hz for space) superimposed on the 4-20 mA signal.

SACA - Smart Automation Certification Alliance Practice Test

SACA - Smart Automation Certification Alliance Practice Test

SACA Process Control and Instrumentation 4